(1) Field of the Invention
The present invention relates to a method of, and an apparatus for, the separation of soot particles from diesel fuel exhaust gases before the separated soot particles are burned.
(2) Description of the Prior Art
All conventional techniques for burning the soot particles contained in diesel fuel exhaust gases operate on the principle of first separating the soot particles in a filter and then burning the separated soot particles. For example, an electrofilter with annular electrodes is used and the relatively large soot particles are separated by a centrifugal separator and returned to the suction inlet with a partial stream of the exhaust gases. It has been found that such soot particles cause an unacceptably high abrasive wear of the pistons and cylinders in the diesel engine. It has also been proposed to use cellular filters with adjoining long filter cells, which preferably have a qaudratic cross section and whose inlets and outlets are alternately closed by a plug. The exhaust gases to be filtered pass through the common porous wall of two adjoining cells while the aerosols cannot pass through the pores of the walls and are deposited in that cell whose inlet is open. Such filters have been made of high temperature resistant ceramic materials and are preferably coated or doped with catalytic substances so that the separated soot particles will be burned at a temperature below 700.degree. C. in the presence of an excess of oxygen. Since such temperatures are reached only when the engine operates at very high speed, considerable deposits producing counter-pressures to the flow of the exchaust gases are built up during the periods when the engine does not operate at very high speed, which reduces the output of the engine in an unfavorable manner. In addition, the pores in the cell walls of the filter are covered by the non-combustible metallic impurities in the soot particles, thus producing a non-reversible counter-pressure build-up in the exhaust gas filter over the long run. Furthermore, the plugs of the outlets are eventually worn down so that the filter in time becomes increasingly more permeable.